There is a fairly extended discussion over on the Climbing forum http://www.trailspace.com/forums/climbing/topics/33979.html about Kilimanjaro climbing guides. You are asking about safaris in Tanzania. Many of the climbing guide services for Kili also run safaris. The comments and advice given in that discussion apply to the safaris as well for the most part. The basic thing is that you have to hire local guides for the parks. If you book from North America or Europe, the booking companies hire the local guides (and charge you their overhead as well).

Take a look at the books recommended in that discussion. The Lonely Planet series are widely available and their advice is pretty dependable.

Thank you for your response. Yes, I did read some of the comments regarding climbs, but you're right, I wasn't thinking that they would apply to safaris as well.

There is a tour group in particular that my family was/is considering using, and I haven't been able to get much information on that tour group. Yes, they do have a website (very limited info, though) and I'm not sure if I feel comfortable going with them without investigating a little more. The company is called Shah Tours, and all correspondence is through e-mail. Ever heard of this particular company?

check some sporting magazine sites like http://www.sportsafield.com/ - also the safari club international would be a good place to check www.safariclub.org/ - as they all deal with sportsmen going to Africa.
You may be able to find others who have dealt with the company you're considering through these resources.
Yes - both the safari club and sports afield are geared towards hunters - no - I don't give a damn about your opinions on hunters or hunting.